Motor-driven closure elements of vehicles are for example window-lifters and sliding roofs. The respective associated motor device is equipped with a position determination facility. This is necessary so that the respective window or sliding roof can be stopped at an intended position. Moreover, such position determination is also necessary to ensure compliance with legal requirements in respect of anti-trap protection.
In known means for position determination for window-lifters, a first-time initialization is implemented during production by running the window up to its upper mechanical stop. This is detected by a control unit and used as reference for later position counting processes. These position counting processes take place during the up and down movement of the window by counting the Hall sensor pulses related to the rotation of the respective drive motor. These pulses are generated on the basis of the rotation of the motor shaft to which a magnet wheel is attached, the latter being provided with alternate sectors and poles of differing polarity in the circumferential direction.
Generally for position determination, two Hall sensors offset by 90° from each other are used. It is therefore possible to determine both the rotational velocity and the direction of rotation.
In order to reduce the costs of the drive, the use of only one single Hall sensor for position determination is already known. In this case this is provided merely for counting the pulses. The information regarding the direction of rotation is derived from the known states of the motor control relays. Inaccuracies in the position determination cannot be ruled out in this system.
If two Hall sensors are used for position determination to avoid the problem of position inaccuracy, then this results in higher system costs, in particular in the motor and in the cable harness.
Apart from systems with Hall sensors, realizing position determination by counting the motor commutator current ripple, as described in DE 197 29 238 C1 for example, is also already known. Position inaccuracy is also inherent in such systems.
Avoiding the problem of position inaccuracy by regularly re-initializing the position determination by always running the window up to the upper mechanical stop or every nth window movement is also already known. However, this has the disadvantage of higher loading of the mechanical system, which in turn results in higher mechanical system costs. Furthermore, this is not always possible. For example, if the window glass is frequently operated and frequently jams without the window fully closing or opening, then re-initialization is not possible.
A method and a device for determining the actual reversal of the direction of rotation of a rotary servo actuator, is known from EP 1 175 598 B1. In this method, an asymmetric rotary encoder disk on the rotor is used to provide speed-proportional pulse trains with interposed reference pulses. These pulses are detected by a single sensor on the stator and evaluated in an evaluator.
Another device for determining the actual reversal of direction of rotation of a reversible rotary actuator is known from DE 10 2005 047 366 A1. This device also uses a rotary encoder disk with an asymmetric coding structure distributed around the periphery of the rotary encoder disk, as well as a single detector which, by sampling the coding structure when the rotary encoder disk rotates, generates a rotor speed-dependent pulse signal. This signal is fed to an evaluator which, by evaluating the pulse edges, determines the actual reversal of the direction of rotation. Said coding structure of the rotary encoder disk is formed by coding sectors having a first sector width and a pair of reference coding sectors having a second sector width.
An actuator for moving power-operated closure elements, in particular windows, partitions or roof elements in motor vehicles, is known from DE 196 33 941 C2. Here the movement of the closure element is realized via a displacement path and with a definable closing force limit when the closure element comes up against an obstacle. At the same time, there is the control dependency of the respective motive force of the closure element corresponding to a previously recorded operational friction force/displacement path diagram and having a friction force that is increased in each case by the permissible closing force.